This inventions relates to methods and apparatus for treatment of congestive heart failure (CHF) by removal of excessive fluids, such as water. In particular, the invention relates to an extracorporeal circuit with minimized blood residence time.
Congestive Heart Failure (CHF) is the only form of heart disease still increasing in frequency. According to the American Heart Association, CHF is the xe2x80x9cDisease of the Next Millenniumxe2x80x9d. CHF is a condition that occurs when the heart becomes damaged and reduces blood flow to the organs of the body. If blood flow decreases sufficiently, kidney function becomes impaired and results in fluid retention, abnormal hormone secretion and increased constriction of blood vessels. The fluid overload and associated clinical symptoms resulting from these physiologic changes are the predominant cause for excessive hospital admissions, terrible quality of life and overwhelming costs to the health care system due to CHF.
One possible method for removal of excessive fluid is mechanical fluid removal employing an extracorporeal circuit with a hemofilter. This method is especially useful if CHF is in its final stage and drug treatment is no longer efficient. Extracorporeal fluid removal is a common method used to treat acute renal disease. Fluid removal treatments are usually combined with either hemodialysis or hemofiltration to also remove solutes normally excreted by the kidney. Currently the most advanced device for this treatment is the PRISMA(trademark) system from Gambro, which comprises an air free extracorporeal circuit consisting of a blood tubing system with integrated filter, a plurality of injection or sampling ports and pressure measuring domes. Although attempts have been made to construct a streamlined flow path, the blood flow passage in the PRISMA(trademark) system still has dead zones where fluid or blood stagnates and resides for a prolonged time while blood is otherwise flowing through the system. Zones of fluid stagnation are especially found in the pressure measuring domes of the PRISMA(trademark) system.
Extracorporeal blood treatment usually requires anticoagulation of blood. The reason for this is the activation of blood coagulation by shear and by contact of blood to the surface of the extracorporeal circuit. After activation of the clotting system, it takes several minutes until a clot forms. If a fluid path contains poorly perfused dead zones where blood stagnates for a longer period, then blood clots will form at these sites and the clots eventually will block the entire circuit. Other causes for the enhanced formation of blood clots are blood-air interfaces and obstructions in the fluid path, e.g., the commonly used xe2x80x9cclotxe2x80x9d filters in drip chambers.
Typically, systemic anticoagulation is used such that anticoagulants are not only in the blood in the extracorporeal circuit, but also in the blood in the patient""s circulation. This use of anticoagulants increases the risk of bleeding by the patient during and after treatment. Local anticoagulation or anticoagulation free treatment has been reported, but is possible only with additional equipment and monitoring.
The common blood accesses for acute treatment with extracorporeal circuits are central venous catheters. The insertion and use of central venous catheters are related to several risks that may result in death or severe impairment. In particular, stenosis of the central vessels after use of catheters, which has been well documented, makes frequent insertion of central venous catheters impossible.
The use of peripheral vein access has not been reported with devices used for extracorporeal blood treatments, such as those described above. Peripheral veins tend to collapse during the withdrawal of blood by an extracorporeal blood circuit. The collapse of a vein would cause the blood circuit to issue frequent alarms that would require continuous observation by trained personnel. Also, extracorporeal systems for the use with adults are designed for blood flows not achievable with peripheral vein access.
An extracorporeal circuit has been designed having an optimized streamlined blood passage that is free of obstructions and dead zones where blood can stagnate. The circuit components, e.g., pressure sensors, in the blood are free of obstructions and do not cause blood to stagnate in the circuit or to undergo substantial flow speed changes. The circuit can be used to treat CHF by continuous filtration of blood using peripheral venous blood access, and with minimal or no anticoagulation.
The extracorporeal circuit may be characterized by the normalized residence volume method, derived from the residence time measurements. The normalized volume parameter is used to characterize the flow characteristics of an extracorporeal circuit independently of the total fluid volume capacity of that circuit. When using the 10% to 90% rise of the output function in the normalized volume diagram, the optimized extracorporeal circuit shows superior performance. The present extracorporeal circuit may be applied to remove excess fluid from a CHF patient allow treatment for up to eight hours using no or minimal anticoagulation.
A practical means to overcome the barriers for the effective treatment of CHF by mechanical fluid removal is described in U.S. application Ser. No. 09/618,759, filed Jul. 18, 2000, entitled xe2x80x9cMethod and Apparatus for Peripheral Vein Fluid Removal in Heart Failurexe2x80x9d, U.S. application Ser. No. 09/660,195 filed Sep. 12, 2000, entitled xe2x80x9cBlood Pump Having Disposable Blood Passage Cartridge With Integrated Pressure Sensors,xe2x80x9d both of which patent applications are incorporated by reference.